In recent years, owing to the demands for higher integration degrees and higher operation rates of LSIs, design rules for semiconductor devices of LSIs are increasingly miniaturized. Along with this trend, the resistivity of transistor gate electrodes used in DRAMs or the like is required to be lower. Accordingly, tungsten (W)-containing films with a low resistivity have come into use for gate electrodes of this kind. For example, a tungsten polycide gate (a multi-layered film of WSi/poly-Si) and a tungsten poly-metal gate (a multi-layered structure of W/WN/poly-Si) with a lower resistivity have attracted attention.
On the other hand, where the tungsten polycide or tungsten poly-metal gate is utilized in a process of manufacturing a gate electrode, the process includes a step of performing selective oxidation of poly-silicon on the side surface of the gate electrode. At this time, in order to perform the selective oxidation of poly-silicon while suppressing generation of tungsten oxide, a microwave plasma processing apparatus of the RLSA (Radial Line Slot Antenna) type is used for this step, because it allows the process to be performed at a low temperature by plasma having a high plasma density and a low electron temperature (for example, Patent Document 1).
In a process of this kind, an Si wafer including tungsten is handled, and thus the process chamber used for the process is contaminated with tungsten. If this process chamber is used for subsequent selective oxidation, tungsten affects the process such that tungsten may be taken into devices as contaminants, and tungsten may hinder the oxidation process and decrease the oxidation rate. Accordingly, it is necessary to perform cleaning of the process chamber used for the process, so as to decrease the contamination level thereof to an acceptable level for manufacturing semiconductor devices.
Conventionally, where cleaning is performed for a process chamber contaminated with tungsten (W), the process chamber is first opened to the atmosphere. Then, components inside the chamber are subjected to wet cleaning by an acid or the like, and further the inner wall of the vacuum chamber is cleaned up by a wiper impregnated with acid, water, or solvent.
However, this cleaning requires a time period for setting the process chamber opened to the atmosphere, a time period for performing the wet cleaning, a time period for performing re-exhaust, a time period for re-conditioning the process chamber after the exhaust, and so forth. These periods sum up into several hours and account for a decrease in throughput.
On the other hand, a dry cleaning method using plasma is also under review. The dry cleaning method using plasma is typically a method of turning a cleaning gas into plasma to remove deposits from inside a chamber.
However, conventionally, it has not yet been successful in utilizing dry cleaning to efficiently clean a process chamber contaminated with metal, such as tungsten (W).
Further, the end point of dry cleaning is difficult to find, and thus time management is utilized to determine the end of cleaning. However, since time management is arranged to terminate cleaning with reference to a preset time, a problem arises such that the cleaning is insufficient or the cleaning time period is too long. If the cleaning is insufficient, troublesome re-cleaning has to be performed, because deposits remaining in a chamber cause contamination. If the cleaning time period is too long, time and energy are wastefully consumed.
Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2000-294550